The invention relates generally to electrical machines, particularly to electrical machines having permanent magnet type rotors. Specific embodiments of the present technique relate to a system and method for magnetization of permanent magnet segments in such rotors.
An electrical machine, such as a motor or a generator, generally includes a rotor disposed within a stator and utilized to convert electrical power to mechanical power or vice versa. Certain electrical machines use permanent magnet type rotors, which reduce the size and enhance the overall efficiency of the machine. Such a rotor generally includes an annular permanent magnet, disposed over a rotor spindle. In certain embodiments, the permanent magnet is a monolithic, hollow, cylindrical member. In larger machines, the permanent magnet is generally formed by assembling a plurality of permanent magnets assembled around a rotor spindle. High speed electrical machines may also include a holding ring or a retaining ring around the permanent magnet assembly to prevent fracturing and scattering of the permanent magnet assembly by centrifugal forces.
Generally, the permanent magnet segments are magnetized prior to assembly on the rotor spindle. For example, the permanent magnet segments are cut and ground to shape from larger unfinished magnet blocks, after which the segments are magnetized individually in a solenoid coil. In certain applications, especially in larger machines, magnetization of the permanent magnet segments is achieved via a magnetization vector proposed by K. Halbach (also known as Halbach magnetization), which, when applied to the surface of the permanent magnets, results in a more sinusoidal shaped flux distribution within the electrical machine, thereby reducing AC harmonic losses and reducing torque ripple, vibration and acoustic noise. The permanent magnet segments are subsequently adhesively bonded to the rotor spindle.
However, assembly of the rotor from pre-magnetized permanent magnet segments may be a cumbersome process, especially in larger electrical machines, as it may be time consuming and unwieldly. The process can involve substantial forcing and aligning by mechanical devices to position and restrain the energized permanent magnet segments. The process is prone to physical accidents if energized permanent magnet blocks escape restraint.
Accordingly, there exists a need for a simpler and efficient technique for magnetization of the permanent magnet segments in electrical machine rotors.